Electronic Thesis and Dissertation Repository

Thesis Format

Monograph

Degree

Master of Science

Program

Civil and Environmental Engineering

Supervisor

Kopp, Gregory A.

Abstract

Effects of crosswind turbulence on the mechanisms and flow structures affecting emissions from non-premixed wake stabilized flames from elevated stacks are investigated. In the current work, two conditions of upstream crossflow are tested to investigate the effects of turbulence on the flame, including the turbulent flow with enhanced freestream turbulence that is generated by a passive grid placed upstream of the burner, and smooth flow with ambient turbulence for baseline comparisons. The experimental method of Mie scattering flow visualization is used to investigate the effects of turbulence. The addition of freestream turbulence has been found to make changes to the flame characteristics and the development of vortical structures in the separated shear layer, which are closely associated with increases in combustion inefficiency. The fuel stripping mechanism was proposed to be responsible for inefficient combustion; a few bits of unburnt fuels are observed to be drawn through adjacent flame pockets, and finally are ejected away from the underside of flame without combustion. The Mie scattering images combined with combustion inefficiency data indicated the bypass-transition in the shear layer plays an important role in the fuel stripping mechanism.

Summary for Lay Audience

Global warming driven by greenhouse gas (GHG) emissions is a serious problem that causes climate change. GHG emissions in Canada increased by 20.9% (126 megatonnes of CO2 equivalent) between 1990 and 2018. One major cause is emission from upstream oil and gas production. Flaring is an environmentally friendly and safe waste gas disposal method. Flaring CH4 (methane) greatly reduces the global warming effects because CH4 has a global warming potential 25 times higher than CO2 (carbon dioxide) based on 100-year effects (Johnson, Kostiuk, & Spangelo, 2011). However, gas flaring is not 100% efficient; incomplete combustion causes unburned fuels to be released into the atmosphere, which are harmful to the environment and human health.

The pollutant emissions from gas flaring have become critical in recent years. Many researchers studied the effects of smooth crosswind velocities on combustion inefficiency, but the fundamental understanding of the effects of crosswind atmospheric turbulence is incomplete. In the current work, the effects of crosswind turbulence are investigated. It is found from flame images that the turbulent flow can change the flame shape and appearance, as well as vortices in the shear layer regions. Those changes are closely related to the mechanism leading to combustion inefficiency.

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